共查询到19条相似文献,搜索用时 411 毫秒
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研究了正交频分复用(OFDM)系统中采用的混合自动重传请求(HARQ)技术,对其性能和实现方案进行了分析;在采用高阶调制时,为均衡同一映射符号内比特可靠性差异采用星座重排方案,并对星座重排技术进行了研究;在典型城区多径信道环境下,对不采用HARQ、采用Type I HARQ、采用Type Ⅲ chase合并的HARQ和采用带有星座重排的Chase合并的HARQ4种方案的误码率和吞吐量性能分别进行了仿真;仿真结果表明,星座重排技术结合Chase合并的HARQ机制是无线通信系统中提高传输质量和吞吐量的一种高效可行的方案. 相似文献
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本文研究了采用16-QAM调制和星座重排的chase合并型高级混合ARQ系统.针对星座重排中比特可靠性的差异.提出一种近似算法逼近软解调输出比特的对数似然比.仿真结果表明,该近似算法能有效降低重传后比特可靠性的差异,且计算复杂度大大降低,提高了系统的性能. 相似文献
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基于FPGA的高阶QAM调制器的实现 总被引:1,自引:0,他引:1
针对全数字正交幅度(QAM)调制技术在数字微波通信系统中的应用,以64QAM为例提出了一种全数字实现的调制系统结构方案,基于QuartusⅡ及Matlab软件开发平台,用原理图和Verilog HDL语言相结合的方法实现了高阶QAM调制器的各个模块的FPGA设计。由于256QAM与64QAM具有相同的矩形星座图,通过修改Verilog HDL程序可以适应256制式的QAM调制。 相似文献
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《电子技术与软件工程》2015,(16)
为应对日益增长的室内数据业务需求,3GPP对LTE-A标准进行了增强,针对室内场景提出LTE-Hi(LTE Hotspot/Indoor)系统。本文给出了自主开发的基于OPNET开发的LTE-Hi系统级动态仿真平台方案,着重介绍了各个网络节点模型以及仿真流程的实现。该平台通过OPNET的离散事件驱动机制进行仿真,支持最高8×8多天线传输以及256-QAM高阶星座调制,能够对LTE-Hi系统性能进行精确有效的评估。 相似文献
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A data predistortion technique with memory for QAM radio systems 总被引:1,自引:0,他引:1
The authors present an efficient data predistortion technique with memory for compensation of high-power amplifier (HPA) nonlinearities in digital microwave radio systems employing quadrature amplitude modulation (QAM) signal formats. A practical implementation method is described which trades off performance against complexity and which makes it possible to implement this kind of predistorter in 256-QAM, and higher-level QAM systems. Using the 16-, 64-, and 256-QAM signal constellations, it is shown that the proposed technique achieves a considerably higher performance than that of conventional memoryless data predistortion of the predistortion technique with memory based on finite-order inverses of nonlinear systems. Specifically, numerical results show that the proposed technique achieves a gain that is in excess of 2 dB over conventional memoryless data predistortion 相似文献
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We propose to investigate the performance of bit-interleaved coded modulation with iterative decoding (BICM-ID) over Rayleigh fading channel by using constellation shaping (CS). The (CS) is implemented by inserting shaping block codes between mapping and channel coding functions, in order to generate non-equiprobable distribution of a 16-ary QAM signal constellation. Simulation results carried out on 2-bit/s/Hz 16-QAM BICM-ID indicate that is possible to obtain a gain of 1.2 dB at a BER of 10-3 compared to the equiprobable 16-QAM BICM-ID schemes. It is also shown that, the error floor level can reduced by applying the signal space diversity technique. 相似文献
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We present a new multilevel coding technique for the quadrature amplitude modulation with a high number of states (64-QAM and 256-QAM). The constellation is partitioned into four subsets, two bits coded with the samebch code selecting the label of each subset. We show that our system, with a double error correctingbch code, gives better results, considering redundancy, decoding simplicity and performance, than the systems known bx now (using the Reed-Solomon code (64,62), the Lee-Nakamura and Hamming codes). Preliminary differential encoding of the two coded bits and utilisation of a transparentbch code can solve the phase ambiguity problem in a simple way. 相似文献
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Blind carrier phase tracking with guaranteed global convergence 总被引:1,自引:0,他引:1
Conventional blind carrier recovery algorithms have been observed to show unstable behaviors for large constellation modulation schemes such as 64-QAM or 256-QAM. We propose a new carrier tracking approach that has guaranteed global convergence. First, we show that the carrier tracking problem is equivalent to a blind source separation problem, which involves the separation of a linear unitary mixture of two independent components that are the real and imaginary parts of the emitted signal. Then, by using a blind source separation procedure, we derive a new and robust carrier tracking algorithm with guaranteed global convergence. Some numerical simulations are provided to illustrate the effectiveness of the proposed method 相似文献
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Abbas Hasan Kattoush Waleed Ameen Mahmoud Al-Jawher Sulaiman M. Abbas Ali Tweij Shaheen 《Wireless Personal Communications》2011,58(4):695-711
In this paper a new method is proposed to perform the N-Radon orthogonal frequency division multiplexing (OFDM), which are equivalent to 4-quadrature amplitude modulation (QAM),
16-QAM, 64-QAM, 256-QAM, ... etc. in spectral efficiency. This non conventional method is proposed in order to reduce the
constellation energy and increase spectral efficiency. The proposed method gives a significant improvement in Bit Error Rate
performance, and keeps bandwidth efficiency and spectrum shape as good as conventional Fast Fourier Transform based OFDM.
The new structure was tested and compared with conventional OFDM for Additive White Gaussian Noise, flat, and multi-path selective
fading channels. Simulation tests were generated for different channels parameters values including multi-path gains vector,
multi-path delay time vector, and maximum Doppler shift. 相似文献
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We present the design and the basic features of variable symbol-rate demodulators for digital TV broadcasting by cable and satellite. The demodulators are fully compliant with the DVB recommendations which were later published as ETSI standards. The satellite demodulator employs the QPSK signal constellation and can handle symbol rates up to 30 Mbaud. The cable demodulator is configurable to operate with all QAM signal formats from 16-QAM to 256-QAM, and handles symbol rates up to 7 Mbaud which is the maximum possible symbol rate in an 8 MHz channel. Both demodulators employ polyphase filtering for variable symbol rate operation and fully-digital carrier recovery loops with an extended frequency acquisition range. In addition, the cable demodulator includes a blind equalizer with smooth transition to a conventional adaptation algorithm after convergence 相似文献
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Two data predistortion techniques are presented that compensate for high-power amplifier (HPA) nonlinearities in digital microwave radio systems by employing quadrature amplitude-modulation (QAM) signal formats. The first one is a T /2-spaced predistortion technique that ensures distortion-free HPA output at two points per symbol interval T . The second is a T /3-spaced predistortion technique which cancels nonlinear distortion at the HPA output at three points per symbol interval. As opposed to conventional data predistortion, which can only compensate for warping of the signal constellation, the new techniques are effective against intersymbol interference. Using the 64- and 256-QAM signal constellations, it is shown that the proposed techniques lead to a very efficient utilization of the available HPA power. It is shown that, of the two techniques, the T /3-spaced data predistortion employs narrower transmit-pulse shaping and achieves higher protection against adjacent-channel interference at the expense of some additional complexity 相似文献
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The performance of 64-QAM and 256-QAM systems amplified by nonlinear power amplifiers (HPAs) is investigated. Two types of HPAs are considered in the analysis. The quadrature crosstalk between the I and Q channels due to AM/AM and AM/PM conversion of the nonlinearities of the HPAs is studied by computer simulation and experimentally. The results reveal that the quadrature crosstalk is mainly caused by AM/PM conversion and that crosstalk is reduced when the output power backoff (OBO) is increased. However, for some HPAs, the crosstalk has the minimum in a certain range of OBO. The power spectra of intermodulation products caused by the nonlinearities of HPAs are shown. In addition, the probability of error performance, P(e), is computed for two types of HPAs and different OBO. A comparison of eye and constellation diagrams for TWTA operating at the different OBO is also given 相似文献